Electricians have long used hand-held wire strippers for basic operations such as wire stripping and cutting. These tools are constructed similarly to a pair of pliers in that they have a pair of elongated members pivotably joined at a pivot pin. The pivot pin defines handles below the pin and jaws above the pin. The jaws typically incorporate wire cutting blades and aligned pairs of semi-circular grooves sized for stripping insulation from wires. The handles fit in the palm of a user's hand. U.S. Pat. No. 6,234,050 shows one type of hand-held wire stripper having ergonomic handles.
Studies of how electricians actually use wire strippers have revealed that the basic wire stripping function is performed by holding the handles of the tool in the palm of the hand with four fingers wrapped around one of the handles. The thumb typically rests on or close to the pivot pin as this is the only portion of the tool that doesn't exhibit appreciable movement during closure of the jaws on a wire. Once the fingers close the handles to cause the jaws to cut a wire's insulation, the resulting slug is usually removed by sideways pivoting motion of the wrist. This flick of the wrist is in the nature of a yawing motion of the wrist, rather than a rolling motion about the forearm or a full sideways translation of the forearm. To effect the yaw of the wrist and overcome the resistance of the slug on the conductor, the thumb is pressed against the pivot pin to push the tool in the desired direction. One of the problems with prior art wire strippers is the pivot pin is not designed to support the thumb and thus creates discomfort in the short run and a real pain in the thumb over long term use. The ends of the pivot pin often present a shape, such as a screw head or a nut, that is not conducive to user comfort. Furthermore, the pin is prone to pinching the thumb during movement of the handles. Repetitive use of the tool, of course, exacerbates these problems. The present invention recognizes the reality of how hand-held wire strippers are used and accommodates the thumb by placing a thumb well over the pivot pin.
Other deficiencies in prior art tools that at first glance seem but minor nuisances can develop into major aggravations over long term use. For example, some electricians prefer a wire stripper that is spring-loaded to open the jaws. During periods of non-use the wire stripper is closed to minimize its size. A locking mechanism is set to retain the tool in the closed position against the bias of the spring. Often the closed tool is slipped into a pocket or a tool belt so the user's hands are free for other tasks. This is usually done with the jaws leading or pointing into the pocket since the user typically is grasping the handles. Unfortunately, the action of sliding the tool into the pocket or tool belt loop often releases the locking mechanism, allowing the spring to open the jaws. This interferes with subsequent removal by spreading the handles apart, making them more difficult to grasp. Also, the open jaws may not allow them to clear a belt loop or otherwise be extracted from a pocket. The present invention resolves this by orienting the lock so that a jaws-first insertion of the tool into a pocket tends to set the lock, not open it.
Another bothersome aspect of prior art tools is the screw cutting apparatus. Sometimes tools of this type have holes in the handles or jaws near the pivot pin for cutting 6–32 and 8–32 size screws to a desired length. Holes in opposite handles or jaws can be aligned with one another when the handles are open so that a screw can be inserted through the aligned holes. Subsequent closing of the handles causes separation of the two holes, thereby shearing off a screw inserted therein. While this arrangement of dual holes does permit cutting screws to a desired length, it requires excessive force to do so.